The invention relates to an electronic fuel injection control system for an internal combustion engine. The system senses both the mass and flow velocity of combustion air for the engine and accordingly controls the amount of fuel injected, without determination from a preprogrammed look-up table according to throttle setting. The invention eliminates the need for a throttle position sensor. The use of air mass and air flow velocity is called a mass flow system.
In a fuel injected engine, it is necessary to know the amount of air going into the engine in order to determine the amount of fuel to be injected, in order to provide the proper air-fuel ratio mixture. In a speed density system, for example as shown in my prior U.S. Pat. No. 4,305,351, hereby incorporated herein by reference, the amount of air going into the engine is determined indirectly by knowing ahead of time the typical amount of air entering the engine for a given throttle setting. The fuel requirements are then programmed in a look-up table memory. This type of system works well if the engine is a constant. However, if the engine is altered, then the look-up table for the fuel requirements must be reprogrammed. This is particularly objectionable in racing applications where the engine may be changed from day to day, or race to race, by providing different compression ratios, cylinder heads, camshafts, etc. The look-up table does not self-correct or automatically track the particular engine at hand.
It is common in marine racing applications to change cylinder heads, seeking higher compression ratios. This changes the operating and horsepower characteristics of the engine, and in turn requires that the speed density system be recalibrated in order to achieve optimum performance. In addition, it has been found in racing applications that the throttle position sensor has a very short life rating. With the high stresses and shock loading typical in racing, particularly on engines running close to 10,000 rpm, it is not uncommon for throttle position sensors to fail within a half hour. It is not unusual to replace the throttle position sensor after every race.
The present invention arose out of marine racing applications, though it is not limited thereto. The invention senses air flow velocity and air mass to control the amount of fuel injected, without determination from a preprogrammed look-up table according to throttle setting. The invention overcome the above noted problems regarding reprogramming and recalibration upon alteration of the engine or use on different engine. The invention also eliminates the need for a throttle position sensor, overcoming the above noted reliability problem.
The present invention provides a mass flow system which determines the amount of air coming into the engine by means of its velocity and mass. With this information, it is known how much fuel the engine needs. The system automatically tracks and self-adjusts to the particular engine at hand, and can be used on an altered engine or on another different engine, and will automatically readjust to the engine's fuel requirements, all without a look-up table. The automatic tracking is also desirable as the engine wears. As piston rings wear, the piston will pull in less air, and the electronic fuel injection control system will automatically lower the amount of fuel injected. Without this automatic adjustment, the fuel-air mixture would become richer.
One manner known in the prior art for measuring air flow is to use a hot film or a hot wire. The denser the air moving by the film, the more heat will be removed from the film. Also, the faster the air moves by the film, the more heat will be removed. The amount of energy needed to maintain a constant temperature of the film is measured, to indicate the amount of heat being pulled off by the air flowing by the film. A drawback of the hot film is that it is a very fragile device. Another problem is that the film must be relatively free of contamination. If there is dirt on the film, the dirt will act as an insulator and will change the measurement. It has also been found that water in the air stream dramatically adversely affects the hot film. Water is much denser than air, and extracts more heat. In marine applications, it is nearly impossible to keep water out of the engine, and hence such system is not suitable therefor.
Another approach known in the prior art for measuring air flow is to use a flapper valve. A spring loaded valve in the air stream is deflected by the air flow, and the amount of deflection measures the air flow. The disadvantage of this approach is that the flapper valve is in the air stream and blocks some of the air, acting like a throttle and reducing maximum horsepower. It has also been found that in rough water applications, the flapper may start oscillating or may even break off because of the shock loads experienced in racing. The rugged environment of marine racing thus rules out the flapper valve approach.
In the present invention, flow velocity of combustion air is measured by sensing air pressure drop across a venturi in the air intake manifold, and the mass of combustion air is measured by sensing air pressure and temperature.